1. Field of the Invention
The present invention relates to a storage box for a cassette for use with a thermal printer.
2. Description of the Prior Art
In a thermal printing process, a dye-bearing donor ribbon is brought into contact with a dye-receiving print sheet at a print zone. Thermal printing is effected by contacting the donor ribbon with a multi-element print head which spans the ribbon in a direction transverse to the direction of ribbon travel. The print head typically comprises a linear array of closely spaced resistive heating elements, each being individually addressable by an applied voltage to heat that portion of the donor ribbon directly opposite and thereby cause dye to be transferred from the ribbon to the print sheet. The print sheet is attached to the surface of a rotatable print drum which advances the print sheet past the print head.
The dye ribbon is in the form of a web-like dye carrier containing a series of spaced frames of different coloured heat-transferable dyes and is spooled on a supply spool. The ribbon is paid out from the supply spool and rewound on a take-up spool. The dye ribbon is difficult to handle since it has typically a thickness in the order of magnitude of ten micrometers only in order not to impede the heat transfer from the heating elements towards the receiver sheet. For that reason, the supply spool and the take-up spool are usually provided in a dedicated cassette which has a central rectangular opening allowing the print head to urge the ribbon in contact with the receiver sheet on the print drum.
The first types of cassettes were made of plastic and were of the disposable type. The convenience for the operator of the printer was high and protection of the vulnerable ribbon was satisfactory.
Environmental requirements put an ever increasing strain on the use of disposable cassettes and so there came of a second type of cassettes which were reloadable and basically had the same configuration as the original disposable ones, but which had a two-part construction allowing their opening and reloading. Supply of a full and a take-up spool occurred in a simple cardboard package.
Then came a third type of cassette which is not a duplication of former plastic ones but which up from the beginning was designed as a reloadable cassette. It is a sturdy, completely open structure and in fact is nothing else than a frame, comprising basically two parallel flanges of sheet metal and interconnecting rods, between which a supply and a take-up spool are rotatably and removably supported. The frame has at its lateral sides handles for its manipulation. Such manipulation is delicate, considering the kind of ribbon loaded in the completely open frame structure. A cassette of the described type is disclosed in our co-pending EP Appl. 92 203 247.9, filed 22 Oct. 1992 and entitled: "Dye ribbon package for use with a thermal printer and a method of loading the reloadable cassette of a thermal printer with a dye ribbon from a dye ribbon package" which corresponds to U.S. Pat. No. 5,415,486.
Yet this cassette does not completely solve the manipulation problem of a dye ribbon for the following reason. Thermal printing is used for producing transparent as well as opaque prints, and this in black-and-white or in colours. These different types of applications require corresponding types of dye ribbons and thus in practice at least three cassettes are used each loaded with a suitable dye ribbon. In use of a printer, an operator can be forced to regularly replace a cassette by another one depending on the type of work being done. Whereas frequent handling of a cassette as such does not raise a problem because of the handles provided, storage of the cassettes does form a point since the spools with dye ribbon are freely exposed and thus accidental touching or soiling by dust can intolerably damage the ribbon.